Multilayer insulation (MLI) is used in applications requiring lightweight, high performance thermal insulation for aerospace applications such as spacecraft, cryogenic propellant tanks including liquid hydrogen tanks for aircraft, cryogenic refrigerators, and instruments. MLI is typically used in a high vacuum (<10−2 Pascal) where its performance exceeds alternative insulations by a factor of ten. However, the heat flow through the MLI is usually the major heat leak in cryogenic systems, so improvements in thermal performance would be desirable.
In cryogenic space propulsion applications, an insulation system that has high performance on orbit is required. However, the insulation must also provide adequate performance during pre-launch and launch to prevent heat gain, boil off of cryogenic propellants, and condensation or frost formation on the insulation outer surface. Also, the insulation is required to have a low mass, so that the payload capacity of the vehicle used to place the system in orbit is not unduly affected.
Current multilayer insulation consists of layers of metalized polymer sheets that are separated by fabric web or net, typically made of silk or polyester. The fabric net is often attached to the polymer sheets only at the edges. The thermal and mechanical contact between the net and sheets is not well controlled and therefore the conductance through the layers is difficult to predictably characterize. The net is a soft fiber material that has a high thermal contact conductance. Use of the insulation within the atmosphere requires a vacuum shell that does not put a compressive load on the insulation. Such a vacuum shell is inherently heavy (on the order of 10 kg/m^2) and difficult to make more lightweight because the shell has to resist buckling under external loading of atmospheric pressure over 10,000 kg force per square meter.
Other MLI technologies using a multi-layer honeycomb sandwich material for structures are light in weight and can be made very rigid relative to their weight. However, the insulation performance of such structures has been less than desired.
Accordingly, there is a need for a lightweight, high performance thermal insulation for critical missions such as NASA's next generation spacecraft for space exploration mission. Insulation that can provide high thermal performance both in-atmosphere and on-orbit (in vacuum) is critical to the success of NASA Exploration spacecraft.